1. Field of the Invention
The present invention relates to a thin-film transistor (TFT), a method of manufacturing the TFT, a TFT substrate having the TFT, and a display device having the TFT substrate. More particularly, the present invention relates to a TFT adapted to a liquid crystal display (LCD) device, a method of manufacturing the TFT, a TFT substrate having the TFT and a display device having the TFT substrate.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) device includes an LCD panel that displays an image using a light-transmitting ratio of liquid crystal molecules, and a backlight assembly disposed below the LCD panel to provide the LCD panel with light.
The LCD panel includes a first substrate, a second substrate facing the first substrate, and a liquid crystal layer interposed between the first and second substrates. The first substrate includes a plurality of thin-film transistors (TFTs). The TFTs include a plurality of pixel transistors electrically connected to a plurality of pixel electrodes, respectively, and a plurality of driving transistors for controlling the pixel transistors. The second substrate has a plurality of color filters formed in a position corresponding to the pixel electrodes.
Each of the TFTs includes a gate electrode, a gate insulation layer formed on the gate electrode, an active layer formed on the gate insulation layer, and source and drain electrodes that are spaced apart from each other on the active layer.
The active layer may include, in general, an amorphous silicon film, a microcrystalline silicon film and a polycrystalline silicon film.
The amorphous silicon film has a lower electron mobility than the microcrystalline silicon film and the polycrystalline silicon film. Although the polycrystalline silicon film has a higher electron mobility than the amorphous silicon film and the microcrystalline silicon film, a manufacturing process of the polycrystalline silicon film may be complicated.
The microcrystalline silicon film is manufactured by a simpler process than the polycrystalline silicon film. The microcrystalline silicon has a higher electric mobility than the amorphous-silicon film. However, microcrystals are not present at the bottom of the microcrystalline silicon film, and are only present at the top of the microcrystalline silicon film. Therefore, when a voltage is applied to the gate electrode to form a channel in a lower portion of the microcrystalline silicon film, electron mobility corresponding to the channel may have a relatively lower value than expected.